The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
This disclosure relates to compositions and methods for treating subterranean formations, in particular, compositions and methods for cementing subterranean wells.
Geopolymers are a novel class of materials that are formed by chemical dissolution and subsequent recondensation of various aluminosilicate oxides and silicates to form an amorphous three-dimensional framework structure. The term geopolymer was proposed and first used by J. Davidovits. His work is described in the following publication: Davidovits, J: “Synthesis of New High-Temperature GeoPolymers for Reinforced Plastics/Composites,” Society of Plastics Engineers, IUPAC International Symposium on Macromolecules, Stockholm (1976). Other terms have been used to describe materials synthesized utilizing a similar chemistry, such as alkali-activated cement, geocement, alkali-bonded ceramic, inorganic polymer, hydroceramic. In the following description, the term geopolymer will be used.
Geopolymers based on aluminosilicates are generally designated as poly(sialate), which is an abbreviation for poly(silicon-oxo-aluminate) or (—Si—O—Al—O—)n (with n being the degree of polymerization). The sialate network consists of SiO4 and AlO4 tetrahedra linked alternately by sharing all the oxygens, with Al3+ and Si4+ in IV-fold coordination with oxygen. Positive ions (Na+, K+, Li+, Ca2+, . . . ) must be present in the framework cavities to balance the charge of Al3+ in IV-fold coordination.
The three-dimensional network (3D) geopolymers are summarized in the table below.
TABLE 1Geopolymers chemical designation (wherein M is a cation such aspotassium, sodium or calcium, and n is a degree of polymerization)Si/AlratioDesignationStructureAbbreviations1Poly(sialate)Mn(—Si—O—Al—O—)n(M)-PS2Poly(sialate-siloxo)Mn(—Si—O—Al—O—Si—O)n(M)-PSS3Poly(sialate-disiloxo)Mn(—Si—O—Al—O—Si—O—Si—O—)n(M)-PSDS
The properties and application fields of geopolymers will depend principally on their chemical structure, and more particularly on the atomic ratio of silicon versus aluminum. Geopolymers have been investigated for use in a number of applications, including as cementing systems within the construction industry, as refractory materials, as coatings, as ceramic precursors and as encapsulants for hazardous and radioactive waste streams. Geopolymers are also referenced as rapid setting and hardening materials. Compared to conventional Portland cement, they typically exhibit superior hardness and chemical stability.
Geopolymer synthesis involves the suspension of solid raw materials, such as the above mentioned aluminosilicates, into a carrier fluid. The fluid-to-solid ratio of this suspension affects properties of the suspension, such as for example, its viscosity and hardening time, and the properties of the hardened material obtained from the same suspension. Adjustment of the viscosity of this geopolymeric suspension without altering the other properties is critical in many applications such as the homogeneous coating thickness, the molding of ceramic pieces or the placement of the cement in a building structure or in well cementing.
Some applications require a control of the thickening time and setting time of the geopolymeric suspension. Well cementing, in particular, implies controlling the consistency of the suspension at various temperatures encountered by the fluid in order to achieve proper fluid placement It entails that thickening and setting times need to be controlled, depending on, for example, temperatures encountered by the fluid during its placement and the geometry of the well.
Several documents disclose the use of geopolymer compositions in the construction industry, each of which is incorporated herein by reference thereto. In particular U.S. Pat. No. 4,509,985 discloses a mineral polymer composition employed for the making of cast or molded products at room temperature, or temperatures generally up to 120° C.; U.S. Pat. No. 4,859,367, U.S. Pat. No. 5,349,118 and U.S. Pat. No. 5,539,140 disclose a geopolymer for solidifying hazardous waste materials and storing them for very long time periods, comparable to certain archeological materials; U.S. Pat. No. 5,356,579, U.S. Pat. No. 5,788,762, U.S. Pat. No. 5,626,665, U.S. Pat. No. 5,635,292 U.S. Pat. No. 5,637,412 and U.S. Pat. No. 5,788,762 disclose cementitious systems with enhanced compressive strengths or low density for construction applications. WO 2005019130 highlights the problem of controlling the setting time of geopolymer systems in the construction industry.
More recently WO 2008017414 A1 and WO 2008017413 A1, describe the application of geopolymers in the oilfield industry, well cementing in particular. These documents state that well cementing involves controlling the mixability, pumpability and stability of the suspension at various temperatures encountered by the fluid in order to achieve proper fluid placement, and controlling the rate at which the suspension sets and hardens. In addition, the solid-to-fluid ratio is adjusted to optimize the density of the suspension, and the mechanical properties and permeability of the hardened material. It is well known that increasing the temperature of a geopolymer suspension will accelerate the setting time. Thus, these documents mention different methods for controlling the thickening time, such as the nature and/or the pH and/or the concentration of the activator, and/or the concentration of the alkali-metal silicate. The accelerative effect may also be mitigated to some extent by choosing an aluminosilicate with lower reactivity (e.g. fly ash). However, these approaches may still be inadequate at the temperatures encountered during well-cementing operations.
Unlike Portland cement, for which hundreds of additives have been developed to modify its performance over a wide range of conditions, the population of additives useful in the context of geopolymers is comparatively sparse. Therefore, despite the valuable contributions of the prior art, there is a continuing need for additives, particularly retarders, that are useful to control the thickening time, setting time or both of geopolymeric systems in the context of well cementing.